1. Field of the Invention
The present invention relates to a head gimbal assembly provided with a magnetic head for writing data signals according to heat-assisted magnetic recording technique, and to a magnetic recording apparatus provided with the head gimbal assembly.
2. Description of the Related Art
As the recording density of a magnetic recording apparatus, such as a magnetic disk apparatus, becomes higher, further improvement has been required in the performance of a thin-film magnetic head and a magnetic recording medium. As the thin-film magnetic head, a composite-type thin-film magnetic head is widely used, which has a stacked structure of a magnetoresistive (MR) element for reading data and an electromagnetic transducer for writing data.
On the other hand, the magnetic recording medium is generally a kind of discontinuous body of magnetic microparticles gathered together. Here, one record bit consists of a plurality of the magnetic microparticles. Therefore, in order to improve the recording density, it is necessary to decrease the size of the magnetic microparticles and reduce irregularity in the boundary of the record bit. However, the decrease in size of the magnetic microparticles raises a problem of degradation of thermal stability of magnetization due to decrease in volume.
As a method of solving this problem of thermal stability, so-called a heat-assisted magnetic recording technique is proposed, in which writing is performed by reducing the anisotropic magnetic field with heat supplied to the magnetic recording medium formed of magnetic material with large KU just before application of the write field. For the heat-assisted magnetic recording technique, for example, US Patent Publication No. 2004/081031 A1 discloses a near-field light probe that generates near-field light for heating by receiving light from a light source, which is formed in contact with the main magnetic pole of a write head for perpendicular magnetic recording in such a way that the irradiated surface of the near-field light probe is perpendicular to the medium surface.
Other various modes of the heat-assisted magnetic recording technique are suggested, however, the present inventors propose a heat-assisted magnetic recording head constituted by joining a light source unit including a light source to the end surface (back surface) opposite to the opposed-to-medium surface of a slider including a write head element. For example, US Patent Publication No. 2008/043360 A1 discloses such a light source unit. The advantages of the above-described heat-assisted magnetic recording head are as follows:
a) The head has an affinity with the conventional manufacturing method of thin-film magnetic heads because the opposed-to-medium surface and the element-integration surface are perpendicular to each other in the slider.
b) The light source can avoid suffering mechanical shock directly during operation because the light source is provided far from the opposed-to-medium surface.
c) The light source such as a laser diode and the head elements can be evaluated independently of each other; thus the degradation of manufacturing yield for obtaining the whole head can be avoided. Whereas, in the case that all the light source and head elements are provided within the slider, the manufacturing yield rate for obtaining the whole head is likely to decrease significantly due to the multiplication of the process yield for the light-source and the process yield for the head elements.
d) The head can be manufactured with reduced man-hour and at low cost, because of no need to provide the head with optical components such as a lens or prism which are required to have much high accuracy, or optical elements having a special structure for connecting optical fibers or the like.
The above-described heat-assisted magnetic recording head is combined with a suspension to construct a head gimbal assembly (HGA). The HGA is a main component for properly reading and writing data from and onto a rotating magnetic recording medium in a magnetic recording apparatus. As an HGA for heat-assisted magnetic recording, for example, US Patent Publication No. 2006/0187564 A1 discloses one embodiment in which a heat-assisted magnetic recording head is attached to a suspension. Moreover, Japanese Patent Publication No. 2006-54474A discloses a multilayer structure having polyimide resin layers for a suspension.
A problem to be solved in the HGA for heat-assisted magnetic recording is to construct a radiation structure for effectively getting away the heat generated from a light source to attain a stable light emitting operation of the light source.
When a laser diode is used as a light source, the p-electrode surface of the laser diode is generally stuck on a substrate to be fixed. This is intended to more efficiently radiate the heat by directly getting the p-electrode into contact with the substrate to use the substrate as a heat-sink, because an active layer, which generates heat mostly during operations of the laser diode, is positioned closer to the p-electrode than an n-electrode. Actually, thermal conductivity of, for example, GaAs that is a typical constituent material of a laser diode, is about 47 W/mK, relatively small, and it is therefore desirable that the active layer is positioned closer to the substrate.
However, the thermal conductivity of, for example, ALTiC (Al2O3—TiC), which is a material generally used as a substrate, is about 25 W/mK, which is approximately one digit smaller than that of AlN (about 200 W/mK), AlN being a material generally used as one of heat-sink materials. Resultantly, it has been very difficult to radiate heat with sufficient quantity even if the p-electrode of the laser diode is stuck to the substrate. When the heat radiation of the laser diode is not enough, the light-emitting operation becomes unstable, and further, the laser diode itself is sometimes possible to be damaged.
Regarding the heat-radiation action on the heat generated in a magnetic head, for example, Black et al. “Thermal Management in Heat-Assisted Magnetic Recording” IEEE TRANSACTIONS ON MAGNETICS, Vol. 43, No. 1, p. 62-66 (2007) and McDaniel et al. “Issues in Heat-Assisted Perpendicular Recording” IEEE TRANSACTIONS ON MAGNETICS, Vol. 39, No. 4, p. 1972-1979 (2003) suggest that it is important to secure a heat flow from an air bearing surface (ABS) of a flying slider toward a magnetic recording medium. From this viewpoint, in the above-described heat-assisted magnetic recording head, the heat radiation through the ABS has not been enough, because the light source is positioned considerably separated apart from the ABS. Therefore, it is important to construct a radiation structure that does not depend only on simple radiation through a substrate.